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May an airplane with folding wings legally taxi on the street?
In order for any vehicle larger than a bicycle to be street legal, it must be registered under the state/province's Department/Bureau of Motor Vehicles as a highway vehicle. There already exist light sport airplanes that have folding wings so they can be parked in a standard automobile parking spot, though the tail might stick out a few feet. However, they are intended to be towed to the airfield and not taxied themselves there.
If one simply slaps turn signals, rear parking lights, brake lights, reversing lights, and side mirrors on such an airplane, does it make it road legal to the point where it can be registered under the DMV or BMV? Since FMVSS crashworthiness only applies to auto manufacturers, it does not apply to custom vehicles like Batman cars and Wienermobiles. That is why custom vehicles can be registered under DMV. Also, the tail number of the aircraft satisfies the FMVSS license plate requirement because it is more conspicuous than a license plate. USPS and other US Federal vehicles use large printed numbers to satisfy that requirement.
If such an aircraft is road legal, it is effectively flying car. This would be super useful for road trips, where the drive to the destination can be a conventional drive on the highway, but the return trip can be a flight in order to save time, all with the same vehicle. Furthermore, one can save a lot of money from not having to rent a hangar space by parking at home.
I live in California, where the vehicle safety and pollution laws are strictest in the USA, and want to know about that specifically. What about the Canadian provinces of British Columbia, Ontario, and Quebec, which are possibly even stricter than California?

Welcome to Aviation Stack Exchange! There will be many roadworthiness requirements that airplanes won't meet if they aren't specifically designed to. The propeller will also be problematic for safety reasons. Also, it might be better to ask this on https://law.stackexchange.com; even though this question is about airplanes, it technically isn't about aviation because it's about the use of airplanes on the ground.

@Someone - This started at law.se. I recommended here. But yes, it does fall into both realms.

@WPNSGuy oh okay, thank you. I hadn't seen it there. @ CoastCityLapse00crashtest in that case, please disregard my prior suggestion of asking on Law SE.

Some people are trying to make the aircraft/car combo work: PAL-V website

Check https://www.gyromotion.eu/ (autogyro with all car street  stuff, no affiliation).

Related: Is it legal to take off from the road?

"There already exist light sport airplanes that have folding wings" - looking at photos of some of them it looks like the wings would create a blind spot on the sides, so you would need to install a pair of van mirrors which will have to fold in when flying. Or some type of blind spot cameras. The likely bigger problem is that the wings will create a large side surface area which will be subject to wind buffeting, which might make keeping a lightweight vehicle centered in the lane a challenge in gusty winds. Although I suppose the vertical stabilizer (and rudder?) might help a little.

The biggest problem isn't mechanical.  It's what do you do when someone runs their car into your $100K+ aircarplane.  Can you afford the collision coverage for it?

I was on Nauru in 1985, and it was the only international airport I have ever seen where you go through security, then cross an ordinary road, before boarding the plane. During my stay I went for a walk, and found a Boeing 737 parked beside the road. So different places have different rules (and things may well have changed in 38 years).

@WayneConrad It is a used light sport aircraft that cost only 40,000 USD. This is just a hypothetical example. It could have been an ultralight aircraft that cost just $25,000 when new (same inflation-adjusted price as Fiesta, Yaris, Fit, and Smart Fortwo before those econoboxes were discontinued in the US). Furthermore, tons of suburban families daily drive a 100K USD SUV, such as a fully loaded Suburban, Expedition EL, and R1S, or a base model Escalade or Navigator, so 100K USD isn't a problem for many people.

@CoastCityLapse00crashtest All that is true.  But there's a big difference in the necessity and cost of repairs between a car and a certified aircraft.  As WPNSGuy's answer says, 'I can render your Cessna illegal to fly with a hammer. A couple of bashes in the wing, and you'll need, at the least, an inspection. Probably replace the applicable surfaces. Do the same with a car, and...meh. It still drives OK.'

@CoastCityLapse00crashtest "If one simply slaps turn signals, rear parking lights, brake lights, reversing lights, and side mirrors on [ ANYTHING ], does it make it road legal to the point where it can be registered under the DMV or BMV"  Of course not. Absolutely not. The question is somewhat nonsensical. It's incredibly difficult / typically simply impossible to get "some home made construction" registered as a real car.

"That is why custom vehicles (the weiner mobile etc) can be registered under DMV"  they're not custom vehicles. They're completely conventional well-known vehicles (almost always "A Ford F-150") with modifications.  (Note that indeed in many jurisdictions, such things are simply totally illegal and unheard of. A trivial example is that in Australia, say, as a rule you can't even 'raise' a pickup truck, as is commonplace in the US. In Austria it's totally illegal to "chip" an engine.)

How do you plan to apply torque to the drive axle?  Halfshaft? Electric?   Will the engine need to be running and if so, how do you manage to stop the prop?   Or will it be guarded?

@Harper-ReinstateMonica The airplane will just taxi on the street, but with its wings unbolted and stowed on the sides or on the roof. No torque will be applied to the axles because it doesn't have a driveshaft. The propeller will have a removable guard to protect external objects from propeller strikes. In fact, the guard will be made soft enough to meet EU pedestrian safety requirements.

@CoastCityLapse00crashtest It seems like you're convinced the answer is "yes, definitely." Give it a try and let us know how it works out! ;)

When driving on roads there is no such category as flying car. You must meet the regulations for the vehicle class in question, and if the vehicle can also fly that is a separate matter.
The most expedient way to do this is to classify the vehicle as a motorcycle. This is defined as a vehicle with no more than three wheels such as this vehicle, the 1800lb Aptera, considered a trike. This is a normal configuration for most aircraft.

The regulations are far less stringent: no crash testing, no EPA (or CARB) emissions/fuel economy testing required, etc. In fact, here is the entire list of FMVSS regs that apply to motorcycles, mopeds or motor driven cycles, including three
wheeled vehicles:

FMVSS No. 106, Brake Hoses
FMVSS No. 108, Lamps, Reflective Devices, and Associated Equipment
FMVSS No. 111, Rearview Mirrors
FMVSS No. 116, Motor Vehicle Brake Fluids
FMVSS No. 119, New Pneumatic Tires for Vehicles Other Than Passenger Cars
FMVSS No. 120, Tire Selection and Rims for Vehicles Other Than Passenger Cars
FMVSS No. 122, Motorcycle Brake System
FMVSS No. 123, Motorcycle Controls and Displays
FMVSS No. 205, Glazing Materials
49 CFR 565, Vehicle Identification Number Content Requirement
49 CFR 574, Tire Identification and Recordkeeping
49 CFR 575.6(a)(2)(I), Consumer Information
49 CFR 576, Record Retention

So slap some wings on an Aptera (if they ever go into production) and go flying. Emissions paranoid places will love you because the aptera is electric, at least on the ground. You might be able to use the included battery for flight with a suitable electric motor and prop.
I'm not a fan of electric aircraft due to weight and flying cars have to make a lot of compromises, but this shows that a road legal vehicle can be aerodynamic and lightweight enough to use as a fuselage. Use of electric wheel motors on the ground means you don't have to have a spinning prop in traffic, and cutting back on battery capacity to accommodate local ground use only might have some chance of working.

Nah, with the included battery good luck getting a 1.5 ton body to fly. by adding wings and fuselage - a cessna skyhawk weighs 1.1 tons dry all inclusive. The Aptera would be 80% dead weight.

@Trish The Aptera was intended as an example only, but you are mistaken in stating that it weighs 3000lb. With the 60kw battery it is 1800lb, less than your skyhawk. That does not include any wings, propulsion or tail. I'm not a fan of electric aircraft and flying cars have to make a lot of compromises, but this shows that a road legal vehicle can be aerodynamic and lightweight. Use of electric wheel motors on the ground means you don't have to have a spinning prop in traffic, and cutting back on battery for local ground use only might have some chance of working.

@Pilothead The basic empty weight of a Skyhawk is less than 1700 pounds. It will be heavier with a pilot of course but the same is true of the Aptera. And 60 kWh is the equivalent of about 10 pounds of avgas. Per the POH a Skyhawk uses about that just for engine start, taxi, and takeoff.

@pilothead With solid-state batteries coming circa 2028 for production automobiles, weight wouldn't be a problem. This is especially since the non-flammability of all-solid state batteries (being made from ceramics/glasses) makes batteries doubling as structural members a safe and practical reality.

Since the Aptera is already practically an airplane fuselage, I wouldn't be surprised if Aptera just attaches wings, propeller(s) driven by compact electric hub motors, and an empennage to the production vehicle planned to be released model year 2025 when solid-state batteries become available later on that make the plane light enough to fly economically. Furthermore, the infotainment system of all modern road vehicles has more than enough computing power to support avionics, so Aptera can also just slap antennas integrated into the windshield that connects directly to the infotainment system.

@Chris LOL no, 60kWh is equivalent to the energy in 10 lbs of gas only for silly comparisons like burning the gas in a space heater vs. powering an electric heater with the battery. ICEs are horrifically inefficient at turning fuel into motion. 60 kWh into a motor is equivalent to more like 30 or 40 lbs of gas into an engine.

@nobody 10 lbs or 30 lbs, the point is it's very little for a Skyhawk. With 30 lbs of fuel you'd be around the legal VFR limit just to do one lap around the pattern!

So remove the battery and solar panels from the Aptera, add an ICS to drive a propeller in flight and produce electricity for the electric motor(s) on the road. Let's add a fuel tank, wings and enough VFR instruments to qualify as an experimental aircraft ... what dry weight are we down to now?

@CoastCityLapse00crashtest Why do you think weight wouldn't  be a problem with solid-state batteries? This article mentions their specific energy as around 400 W-h/kg. The specific energy of most hydrocarbon fuels is around 12,000-13,000 W-h/kg and Lithium metal batteries are around 500. We are minimally decades from having a production-ready battery chemistry that can come close to rivaling hydrocarbon fuels for specific energy at the scale of a vehicle, nevermind certified for aviation.

@reirab The thing is, technological inventions are unpredictable. Sure, innovation is continual refinement, which happens at a relatively predictable rate. However, inventions totally change the world once it is practically commercially deployed. After all, no one thought how electricity would revolutionize the world until electromagnetism was accidentally discovered, which made electricity generation quick and economical. With solid-state batteries, someone could accidentally discover tomorrow a chemistry that gets the same specific energy as hydrocarbons as enabled by high EN difference.

@CoastCityLapse00crashtest Technology will advance for sure, but, in relatively mature fields, the rate of advancement is more predictable than you might think. It is exceptionally unlikely that someone will discover a battery chemistry that rivals hydrocarbon fuels soon that can be scaled to use for vehicles while also being commercially viable to produce and sufficiently stable for safe use in vehicles that often crash into each other, let alone vehicles that fly. It's not impossible, but it's exceptionally unlikely to happen soon.

Unlikely. Some problems:

Putting additional lights on vehicles is illegal per CVC 24003 (California Vehicle Code). You'd need an aircraft with no navigation lights, landing light, etc.
Per CVC 26311, every wheel needs brakes.
Smog testing is probably an issue unless the airframe is old enough to be exempted.
CVC 27200 prescribes noise limits, which many aircraft would not comply with.
CVC 27400 forbids drivers from wearing headphones. This kind of fits in with the last one- pilots wear headsets for a reason!
Brakes are likely a problem. Motor vehicles are required to have service brakes and parking brakes, and they must be redundant in specific ways that aircraft brakes may not be. The maximum stopping distances may also be problematic.
You need windshield wipers.
You need a windshield constructed of "safety glazing material." Yours may or may not be already, but aircraft windshields are not required to be.

I'm sure this list is not exhaustive.
From a practical standpoint it would be a bad road vehicle, since it would be slow, have poor gas mileage, kick up rocks something awful, and have a spinny blade of death on it that will badly damage anything it touches but also can do thousands of dollars worth of damage to itself if it so much as hits a rock.

... or if the spinny blade of death gets hit by someone else's rock.  Worse than one more chip in the windshield, for both the vehicle and whatever catches the ricochet.

One can just turn off the navigation lights in order to comply with CVC 24003. Just installing them isn't a problem because commercial vehicles have other lights, especially advertisement screens on top of taxis and ride hailing vehicles. Aren't all wheels braked on an airplane, thus complying with CVC 26311? Airplanes obviously have service brakes for landing. Don't they also have parking brakes for the apron and hangar?

This also assumes the airplane not only meets CARB LEV III, but also is a SULEV that can take 87 AKI octane regular unleaded MoGas (in addition to leaded 100LL RON AvGas) so that it meets the CARB requirement when using that fuel. Airplanes are much quieter when taxiing because the propellor spins slower, so CVC 27200 shouldn't be an issue. Also, headphones won't be used when cruising on public roads because it is not loud enough to warrant that. It is probably only as loud as diesel engine when inside the cockpit, so CVC 27400 shouldn't be a problem.

Also, most airplanes have a windshield because they are able to travel at high speeds. In fact, they have to meet much more stringent requirements. Obviously, those airplanes also have windshield wipers. With regards to headlights, don't landing lights comply with the requirement with highway high beam headlights? If low beans are also required, can't one just add a dinmer circuit?

Airplanes rely on the air to travel, so they have a much lower drag coefficient than cars. So, shouldn't they get better gas mileage when taxiing/driving? Also, is the propeller powerful enough to kick up rocks when it only on taxi throttle? Regarding the spinning blade of death, one can also install a removable cowling just like with pedestal fans to protect external people. Then at the airfield, one can just remove and stow the cowling so that it does not interfere with the aerodynamics of flight.

@CoastCityLapse00crashtest Most aircraft have brakes on the mains but not on the nosewheel/tailwheel. Airplanes are quieter while taxiing slowly but they're still pretty darn loud and extremely loud at freeway speeds. Airplanes may or may not have a lower drag coefficient but using a propeller to drag yourself across the ground is really, really inefficient. The propeller can easily kick up rocks even at taxi throttle, but in any case you're going to be at quite a bit higher throttle to be at "reasonable road vehicle" speeds.

Aircraft have parking brakes, but typically all they do is actuate the service brakes. CA vehicle code requires that no single point of failure outside of the wheel brake assembly itself can take out both the service and parking brakes. Aircraft have no such requirement. A cowling helps with the spinny blade of death but makes your gas mileage even worse and poses problems for visibility.

@CamilleGoudeseune I take offense to that. It is a spinny blade of life...for the pilot!

@CoastCityLapse00crashtest "So, shouldn't they get better gas mileage when taxiing/driving?" No. Slow taxi speeds make the drag advantage of airplanes relative to cars irrelevant. Propellers also have inferior coupling for momentum transfer on the ground compared to driven wheels. Airplane engines and propellers are also optimized for high efficiency at flight speeds with little attention, if any, on the efficiency while taxiing. Indeed, taxxing efficiency is gladly sacrificed for flight efficiency.

@CoastCityLapse00crashtest In other words, airplanes have terrible TERRIBLE efficiency on the ground.

@CoastCityLapse00crashtest "Obviously, those airplanes also have windshield wipers." Nope! Windshield wipers are unusual in general aviation aircraft. They aren't that useful in flight and even in airliners that have them they're mainly used while on the ground.

It looks like someone is seriously underestimating the complexity of this enterprise.

I wouldn't be surprised if Aptera just attaches wings, propeller

Aptera can also just slap antennas integrated into the windshield that connects directly to the infotainment system

If we consider the above mentioned Aptera car, and a similar weight Cessna 172...
The wingspan of the Skyhawk is 11 meters. Subtract the fuselage from that, and you end up with wings about 4.5 meters. Which is the full length of the Aptera at 4.5 meters. So where do you put these when driving around town? Remember, they can't obstruct visibility.
In both realms, the vehicle is hauling around extra weight. On the ground, the flight control surfaces and prop. In the air, roadable suspension. A car can generally withstand a big pothole at 50mph. Not good for the car, but not critical. Go ahead and hit that same pothole at 50mph with the front wheel of the Cessna.
Crashworthiness? I can render your Cessna illegal to fly with a hammer. A couple of bashes in the wing, and you'll need, at the least, an inspection. Probably replace the applicable surfaces. Do the same with a car, and...meh. It still drives OK.
Can this be done? Probably. But it will NOT be cheap or easy.
A flyable Aptera will be significantly heavier than its road counterpart.
FAA, NHTSA, state inspections, all will come into play.
In response to the comment on 'visibility', here is a pic of an Aptera, and the Aptera with an overlay of a Cessna 172 wing. Pretty much to scale, both at 4.5m long.
A wing that size is needed to get an aircraft of that weight and power in the air.

Aptera pic from TheVerge.
Wing planform from WikiPedia

Yes, a few bashes of the flight control surfaces will render the plane inoperable. However, bashes that are hard enough to dent structural metal are uncommon enough that it isn't a problem. If they were such a huge problem, then bush planes wouldn't exist because they need to land on open fields.

Also, the wings on an Aptera won't obstruct the legally required visibility because even with them folded up on the side, the visibility is still better than with people with 2.5 and 3.5 ton lifted pickup trucks.

Arranged with intent you could obstruct the view with a school lunch tray.)

@Pilothead - Just going by the commenters statement of "folded up on the side". A lunch tray, you could put anywhere. A thing that is larger than the car...not so much.

@CoastCityLapse00crashtest Not sure that I understand your comments about lifted trucks. You can see quite well to the sides from those. It's everyone else who has a problem seeing past you.

In response to the picture, the wing will be unbolted and stowed longitudinally on top of the wing box the roof, where it will also not obstruct the doors. I don't know how heavy each wing is, but if each are only 100 pounds or less, then the 2 occupants can simply lift them on top of the roof after unbolting. The weight of even a pneumatic torque wrench and air compressor powering it are proportionally negligible to the airplane, so even that will be carried on-board. Of course, a hand torque wrench will be much more lightweight.

I suppose you'd want to take the wings apart. Putting a purpose-made large airfoil on top of your car seems like an incredible way to crash your car on a gusty day!

Put the wings on top? I can't imagine they weigh less that 200lbs each. And oh yeah...the top is where the Aptera solar panels are.

Here is where Aska put the wings: https://newatlas.com/aircraft/aska-a5-vtol-flying-car/

Sure, the CAA (FAA precursor) certified the Aerocar in 1956 and 6 examples were actually produced with folding wings and a road capable car body. There is still at least one that is airworthy. Granted the road regulations at the time we not quite the same as today.
If its gas or powerplant your worried about, the Porsche 3.2L Carrera engine was at one point certified for flight and there are MoGas conversions for common aviation engines out there. There are also aircraft running more modern Jet-A (read diesel) engines that you could use to build such a craft.
Dealing with the DOT to get it passed all the certifications for safety and keeping it light enough to be a functional airplane is going to be tricky at best but there is nothing explicitly preventing it.
However you might not be able to park it at home and you likely cant just land anywhere even if you "think" its for landing.

Fortunately, keeping it light enough to fly while complying with even DOT crashworthiness regulations shouldn't be a problem. That is because DOT regulations are regarding property damage and occupant protection of the vehicle against a stationary object. Since the plane has to be so lightweight to fly anyway, it'll only have fairly small inertial forces that it has to resist at the speeds the 5-mph bumper and 30-mph crash tests are done at. Furthermore, since the 1990s, the bumper requirement has been lowered to 2.5 mph. I wouldn't be surprised if an unmodified airplane aces all crash tests.

On the other hand, making a rail vehicle with folding wings that runs with freight trains that can also fly would be next to impossible without the chassis being completely made out of carbon fibre or titanium alloys. That is because the FRA has long required a buff strength of 800,000 pounds. Since 2020, however, the FRA has required PTC on all railroads, and the buff strength requirement with PTC is the EU standard of 300,000 lb. So, even a stainless steel airplane with folding wings can also be FRA-compliant under current engineering methods, though likely with poor gas mileage when flying.

Most foldable-wing aircraft aren't street legal, however, the Terrafugia Transition does have this as a design goal. It was announced in 2006 and its first flight was in 2009. Its first delivery was planned for 2011... and that still hasn't happened, nor is there even currently a firm delivery timeline. It did receive a Light-Sport Aircraft Airworthiness Certificate from the FAA in 2021, but then the company soon after announced that it was closing down its operations in the U.S. and moving to China. I haven't heard any updates on them since then.
Meeting the requirements to be legal to drive on streets in the U.S. while keeping its weight low enough to be reasonable for an airplane has been a huge challenge, to say the least.

It could simply be that the company is not well-funded due to lack of investors rather than being an engineering challenge. After all, being able to start commercial production is way, way harder than engineering a hand-built one that works as intended. That is because production line equipment is super expensive.

@CoastCityLapse00crashtest The problem for them has always been engineering, specifically, getting it to be street-legal while also able to fly with reasonable efficiency. Actually fabricating it is relatively cheap compared to designing it and getting it simultaneously certified for both flight and driving on roads. This is pretty much always the case with aviation, which is why manufacturers are still building aircraft based on designs originally certified in the 50s or 60s. (Engineer who has worked as such at one of the world's most capable aviation R&D testing facilities here.)

@CoastCityLapse00crashtest - It could also be that you are simply applying copious amounts of handwavium to the significant engineering and regulatory issues. No one has said this is "impossible". But it ain't easy or cheap.

authors: Vladimir F Героям слава


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How to estimate the time to intercept for homing missiles?
I have been reading the book Tactical and Strategic Missile Guidance by Zarchan, and a notice that he frequently uses the time to intercept $t_{go}$, and in his simulations he fixes the final time.
My question is if $t_{go}$ also is used in practice, and if it is not the case  what is done instead?
The reason for me asking this is that I have doubts about the practicality of estimating $t_{go}$ as it could change dramatically if the target does an unexpected manoeuvre. Additionally estimating $t_{go}$ requires that we compute a predicted impact point which seems cumbersome in an endgame scenario compared to proportional navigation on the form $a_c = N V_c \dot{\lambda}$. Any references to how $t_{go}$ can be computed is also appreciated.

Boringly I suspect the answer to this is not going to be found on the public parts of the internet, however assuming steady course and speed is right for a large number of cases (drone/unaware human), and attempts to predict likely target response would be very prone to gaming/countermeasures.

That makes sense @GremlinWranger I know from experience that certain missile has a lot of stuff going on behind the scenes, but I was afraid I was completely overlooking something basic

@pedernv perhaps I should add to my answer that I frequenly saw this value used in missile simulation, although in missile guidance and control it is still used. Nevertheless the concept of calculation is exactly as I laid out below.

Could you re-phrase 'if  also is used in practice, and if it is not the case what is done instead'? That might be perfectly expressed in a dedicated field of maths, but how could it work in general English?

General
Knowing the time-to-go ($t_{go}$) is essential for advanced missile systems, simply because it defines which phase of the intercept the missile is in. This helps to inform logic and guidance decisions as well as how aggressive they are, which in turn shall maximize the probability of intercept compared to simpler algorithms such as proportional guidance.
Application examples
Such logic decisions may be for example when to switch on the missiles active radar system, which in turn might alert your enemy of your presence, which motivates to do that as late as possible. The AMRAAM missile uses such a system. Other missiles change their flight behaviour for example the MBDA Meteor throttles up and down to optimize its energy when reaching its target and even changes its control strategy (bank-to-turn for skid-to-turn) when it is about to hit its target even though that will starve its ramjet engine. Another example is that of a so-called "loft" whereby long-range missiles loft their trajectory to fly through upper parts of the atmosphere in order to take advantage of lower air-drag. Again this kind of behaviour cannot be realized without the compution of your targeted impact point and therefore an explicit knowledge of $t_{go}$.
Comparison to proportional guidance
Concerning your doubts about "practicality" of such systems:

Keep in mind that these are computer-controlled missiles with (in case of modern missiles) quite a lot of computing power. It is no different to the missile if it has to perform such calculations during its flight or in the endgame as long as there is enough computing power available (which of course was validated by the designers beforehand).
You imply that the proportional navigation would be the better solution which would negate the need for the computation of $t_{go}$. As given by the examples above, $t_{go}$ can be used to increase the chance of hitting a target. Additionally proportional navigation is not perfect either. For example, if you employ PN against a target very far away which only maneuvers slightly (for example by executing a very minor sinusoid motion) your target point will move very dramatically. This results in great maneuvering on the side of the interceptor missile as you try to keep up with this target point. This excessive maneuvers leads to the missile bleeding off a lot of its energy. Allegedly, this happend with Patriot missile defending against Iraqi modified scud missiles which became unstable in the air, however I cannot find the source in the moment. The estimation of $t_{go}$ could inform a decision to adapt your guidance behaviour in order to rule out premature energy loss in midcourse flight.

How to compute $t_{go}$
It is as simple as y dividing your velocity by remaining distance $t_{go} = \frac{x_{go}}{V_{missile}}$. The trick is to know these to parameters over your flight. Modern missile such as the AMRAAM explicitly calculate their trajectory over their flight path until the predicted point of intercept and therefore know exactly how far they intend to fly. From this they can then explicitly calculate how long they will fly. This is computationally expensive, however as stated before modern missile do contain the necessary computing power to carry out these kinds of calculations and they use it! For example look at the different flight profiles of a Javelin missile or read around a bit on the different modes and functionalities of modern missiles, you will be amazed of what kind of complex designs and logic trees these include.

I tried to rewrite my answer such that it better focuses on the question. Please comment if something is still not on point enough.

Please comment, if my answer missed a spot, or something is unclear. I tried to formulate this as clearly as possible, but from the lack of upvotes I have doubts if I achieved my goal.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

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What specific improvements were made in supercritical airfoil design from 1980 - 2000?
I originally asked a question (Comparisons between the A340 and 747-200 wing: sweep angle and span) about the technological developments which allowed the Airbus A340 to have a wing with greater aspect ratio and lower sweep than the Boeing 747-200 wing, despite being designed to carry roughly the same number of passengers. @Koyovis graciously replied that a lot of the ability to design a lower-sweep and higher AR wing was a result of supercritical airfoil development. However, I had a follow-up question that I was encouraged by other commentators to post directly.
As far as I'm aware, the first supercritical sections were introduced on the generation of aircraft launched in the late 70s - early 80s (767, 757, A300, A310). The Airbus A340, along with the 330 and 777 however were launched a decade later, in the late-80s - early 90s.
I am curious whether the airfoils on these latter aircraft incorporated any improvements to their supercritical sections over the late-70s - early-80s generation of aircraft? If so, I'm curious as to what specific improvements were made?

I can't provide any data, but my understanding is the main effort has been to improve stall behaviour. SC airfoils suffered from laminar bubbles at the LE with LE initiated flow separation at stall = holy cow when it goes.  This is why some airplanes like the CRJs have stick pushers.  Newer designs have tamed that behaviour somewhat.

Some formatting always helps. What is now the first paragraph could simply be reduced to "As a follow up to [this question]..." Anyone who clicks the link can read through the Q, the As, and comments to see how you got to this one if they're interested.

Mmh, I'm not that sure that lower swept angle and/or higher aspect ratio are mainly due to a switch toward supercritical airfoils. For a jetliner, OEI climb at takeoff normally drives the choice of the AR, while CG location, weight and pitch and lateral stability drive the choice of the sweep angle.

Note, I found what I believe to be a pretty good answer to my question. As a bit of context, the basic supercritical airfoil design was created in the early 1970s by Richard Whitcomb. I was curious whether the airfoils of ~1990 and beyond, because they were designed using much more advanced CFD tools than Whitcomb's sections were designed with, had improved performance, despite embodying the basic supercritical ideas (which were, generate a region of supersonic lift, weaken the shock wave, move it to the rear, generate lift from the aft using increased camber).
The following image is taken from a lecture given by Frank Ogilvie, the Chief Aerodynamicist on the Airbus A380, at Cranfield University on transonic wing design. He goes through the evolution of HSA (Hawker Siddeley Aviation) and BAC (British Aerospace Corporation) outboard airfoils found on various Airbus aircraft  in the 1970s and 80s. The lecture can be found on Scribd, but you need an account to access it.

You can clearly see how, in tandem with increasing complexity of CFD codes (from no transonic CFD methods on the A300 to transonic small perturbation methods for the A310 to 3D viscous-coupled full potential codes + inverse design methodologies for the A330/340) the pressure distributions associated with the outboard sections of the wings became more aggressive. The shocks became weaker and they were pushed from 40% of chord to around 55% of chord. This translates to greater lifting performance for a given drag.
Also, note - the reason the A320 airfoils are less aggressive is because they had less space to incorporate the high-lift system on a smaller wing. That's why I have focused on the wide-bodies.

Basic work on transsonic airfoils was performed as early as 1940 by K. A. Kawalki in Germany when it was found that inverted airfoils performed better at transsonic speed. Also, the A310 wing is based on a design by Airbus Bremen which was proposed after the Hawker Siddeley design for the A310 wing proved to be mediocre. To save face, Hawker Siddeley used the Bremen design and sold it as their own. Next, the US sued Airbus for patent infringement when the A310 came out with its supercritical wing, only to lose the case because of the earlier work by Kawalki.

Do you have a source for this? I'm pretty sure J.A. Jupp and Dykins would disagree with this. See this lecture on their A310 design efforts - they depict the airfoil as a natural development of Pearcey's "Peaky" airfoils that were used on the A300: https://www.jstor.org/stable/2398246?seq=11#metadata_info_tab_contents

Though I will say, I don't disagree that there have been some conflicts between Bremen and the UK teams in the past. I interviewed an aerodynamicist from Airbus currently and he talked about the big fight over including variable-camber on the A340 wing (eventually it was not included). The A340 wing was also a competition between Bremen and the HSA team.

Nothing in the linked article contradicts what I said. It is only selective in what is reported. Also revealing it its way: The achievement by Vickers with their VC-10 wing is not credited, although it was the best of its time. BTW, Figure 8 demonstrates a lack of understanding what drives maximum subsonic lift. I'm not impressed.

What you are looking for are called Phase 3 airfoils.
While initial research focused on avoiding a shock completely at one specific operating point of the airfoil (Phase 1, in the 1960s), Phase 2 airfoils accepted weak shocks for the benefit of a wider angle of attack range in which that shock could be kept weak, so the result could tolerate small deviations from the ideal operating point (roughly in the 1970s).
On the more recent designs (1980s and 90s) another small lift contribution results from a slower pressure drop on the forward edge of the lower side pressure distribution (the forward lower-surface undercutting of Phase 3 airfoils). This gives slightly more lift at the same angle of attack and also lowers the pitching moment of supercritical airfoils.

Effect of forward lower surface undercutting, from NASA Technical Paper 2969.
The reason for the higher aspect ratio of the A340 has little to do with supercritical airfoils but results from more efficient engines.

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How does radar receive Mode C information?
I know primary radar of ASR can determine only slant range, so by using Mode C transponder, ATC can know the altitude of aircraft.
And I found that if altimeter setting of radar is changed, displayed altitude also be changed.
So I guess that Mode C transponder can deliver only pressure information not altitude information. So Radar convert this pressure information to altitide information referring to radar altimiter setting. And it is not important what altimeter seeting pilot set.
Is it correct?

Mode C transponders transmit QNE altitude (flight level). The FL can be provided by a blind encoder or an encoding altimeter. They are built to provide, in the US, the FL with an accuracy of 125 ft, the pilot has no action on the setting.

Correct.  Mode C responses include the pressure altitude.  This means that many installations use a separate altitude encoder that has no barometric settings.
Whether it is integrated or a separate unit, the kollsman setting does not change the pressure altitude reported.
From http://www.faraim.org/aim/aim-4-03-14-133.html

Mode C Veil. [...]  Unless otherwise authorized by ATC, aircraft
  operating within this airspace must be equipped with automatic pressure
  altitude reporting equipment having Mode C capability.

Thanks. Does 'pressure altitude' mean the altitude in 2992inch? I mean, no matter what pilot sets altimeter setting, Mode C sends altitude information by converting as standard atimosphere.

Yes.  https://aviation.stackexchange.com/questions/8168/where-is-the-official-definition-of-pressure-altitude

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text:
MD81: Why are there so many lights on the fuselage?
Looking at this photo I can see lots of lights on the fuselage of this MD81. It can't be a reflection, can it?

Source: Airliners.net
Why are there so many lights?

For what I can see, the spot of light below the windows is a reflection of the wingtip light.

Are the other lights simply interior lights visible through the windows perhaps?

Does the smoke qualify for ground-ɕheɱtrᶏil? It's a trᶏil, and it's ɕheɱical...

There are a couple of close votes on this: I'm voting to leave open as it does appear to be a fair question relating to "Are these lights part of the aircraft, or an optical illusion" which would seem to be on-topic to me?

I think they are reflection from some light posts in the background environment (green line above the blue "horizon" light), and the reflection of the wingtip position light.

The one you circled in red is an actual light, to illuminate the wing leading edge. I think you are right about the rest though.

@fooot Interesting! Is that for in-flight inspection purposes, or?

I'd say they're reflections. You can see the reflection of a building or something like it on the fuselage, and if you look close enough, you can see the poles of the 2 first lights.
Also most of them are at or near the windows' corners. There aren't any housings or mounts to lights on those spots.

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text:
How can the canard configuration increase the aircraft's maneuverability?
I know that in many of the fighter jets, there are canard configurations like in F16, SAAB Gripen etc and heard they increase the aircraft's maneuverability. Can anyone explains how a canard helps in increasing it?

They form a vortex which causes a pressure drop on the main wing which allows the aircraft to fly at 50 degree angles without stalling.

@Ethan, you can do the same with leading edge extensions. The advantage for manoeuvrability is mainly in the way longitudinal stability works.

@Simon that answer provides the advantages of unstable canard but my question is like how canard increases the maneuverability i.e what additional things are given by canard that are included in the design? I am not sure if i am able to explain what i am looking for.

F16 with canards?!?

Canards don't provide any advantage. Having an instable aircraft (with the CG being not between the wings center of lift and the tail horizontal stabilizers) gives more maneuverability, this is what such aircraft exist. But this requires canards for stabilization. Canards are required for maneuverability, but they are not the cause of it.


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How can we deflect a laser beam from the windshield of a small aircraft?
If someone is pointing a Laser beam on the cockpit of a small low flying aircraft, what kind of hardware can be deployed near the windshield to deflect it?

Why a small airplane as opposed to a large one?

small planes are more prone as they fly low and are more visible than the larger ones..   Larger ones are also prone nut when they are on their descent...

I have to disagree with you @NitinG. Most light airplanes fly high enough that hitting one with a laser would be challenging, all airplanes are most vulnerable to lasers on approach and takeoff as that's when they are lowest and slowest.

@Pondlife not really, they are all about static shielding, this question is about "deploying". I mentioned those in my answer because I received comments asking me to address the point.

@Federico I see your point, but to me all these questions are simply asking the same thing: how can we prevent laser strikes affecting the pilot/aircraft?

Laser light is light: if you deflect the laser, you also deflect other light sources, hence you effectively blind the pilot.
You have then achieved the result of reducing the field of vision of the pilot.
EDIT
To address your comment.

but that would be momentarily but the laser beam can actually blind the pilot completely or can create injury. So, i feel may be deflection is a better idea as it will deflect light only for some time..

how? laser travels at the speed of light, what are you trying to achieve? Blocking the light before it reaches the pilot? Blocking it afterwards? (for a pilot to be blinded, a few milliseconds are enough, given a powerful enough laser source)
EDIT 2.0
Since the above seems not to be clear enough, I will try to express this in other words.
No matter the method of your choosing, laser light travels at the speed of light: by the time you detect it, and then block (or reflect, diffuse, selectively filter) it, the pilot might be already blinded.
If your idea involves the use of passive methods (windshield coatings and similar) see here (and here) why they are a bad idea.

but that would be momentarily but the laser beam can actually blind the pilot completely or can create injury. So, i feel may be deflection is a better idea as it will deflect light only for some time..

@NitinG see edit

It's possible to block some light without blocking all of it. There are filters for specific ranges of frequencies.

@Steve yes, but then you need to know the frequency and "deploy" (as the question asks) a different filter for each (or almost) different laser

@Federico What about diffusion instead of deflection?

@called2voyage that's not what the question asked, but the end effect would not change much. You would blur out everything. Technically it is not blinding, but practically would not be much different.

@Federico Yes, the asker didn't technically ask that, but the goal is to prevent laser causing negative effects (i.e. blinding) in the cockpit. Active diffusion systems are possible where the diffusion would be concentrated where the laser was hitting the windshield, but the rest of the windshield would be less diffused so everything wasn't blurred out. I don't know if this is technically feasible yet or even if it is desirable (certainly, I'm not sure how one would defend against deliberate attempts to blur out the windshield), but I think it is worth addressing.

As mentioned by others, the issue is that lasers are light. If you block too much light, you can't see out.  OTOH, one key feature of lasers are that they operate at specific frequencies, so one solution is a spectral filter that blocks the frequencies used by the most common lasers.  (This technology has been around for about 30 years.)
Integrating the filters into a windscreen would be very expensive.  Using film would likely have certification and maintenance issues, so it's not really practical for a windscreen installation.
A better solution is for pilots to wear laser-protective eyewear containing lenses with the appropriate filtering.

with the appropriate filtering and how would you decide which filtering is appropriate? (in particular, which bandwidth you have to block?)

Two years ago (maybe unsuccessful): Airbus to test windscreen anti-laser film.


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What caused the loss of "everything" on Swiftair Flight QY-2939?
I found this from a youtube video, and more info from this avherald article.
One of the pilots declares an emergency because right after takeoff they lost "everything", as in all instruments. ATC managed to steer them back to a safe landing.
This was 2016 Nov 17, in Ireland, on a Boeing 737-400. What on Earth could cause the loss of all instruments? From what I gathered online, the plane was not struck by lightning or going through bad weather.

Related, though mostly discusses effects, rather than causes: http://aviation.stackexchange.com/questions/35920/how-can-pilots-lacking-instruments-interpret-vectors-given-by-atc

Without an accident report to go on, we can't know what caused the situation they had.  In fact, from the two links that were posted, we don't REALLY know exactly what they had.  There is the description "we lost everything" from the radio, but that isn't consistent with the statement that they were able to fly headings.
So what follows is a comment on the possible, rather than a statement of what DID occur.
What I can piece together is that they seem to have lost their pitot-static system.  This would remove the airspeed and altitude from all displays, but would leave heading and attitude unaffected.  It would also allow them to fly an ILS approach, with distance from the runway and the on-glideslope indication giving them a way to approximate altitude on final.
There are comments about them climbing to VMC, which strongly implies that they had attitude instruments available.  Likewise, the comment about flying headings would suggest that they had INS information available, since the INS drives the heading indications in the 737-400.  Yes, they could fly headings off the wet compass, but that wouldn't give them attitude information, which they seem to have had.
I don't think the descriptions are consistent with losing the displays in the aircraft, because losing the EFIS displays in an EFIS 737-400 would mean they'd use the analog standby attitude indicator, but the analog airspeed & altitude indications would likewise be available.
Based on all of this, my best guess is that the "we've lost everything" statement is more a reference to having lost all airspeed and altitude displays (along with some other data, including a fair bit of the FMC data that becomes invalid when the FMC doesn't have wind data to work with).  Was the statement a perfectly precise & exact description of the loss of only (only!) the pitot/static instruments?  Not really, but in the stress of the moment it's entirely understandable that what gets said doesn't exactly match what you mean.
In a case like this, the lack of good airspeed information would be the biggest problem, although with reasonably light winds, GPS/INS groundspeed can be a reasonable proxy for your airspeed, and you're flying known pitch/power settings anyway.  Also working in their favor, they seem to have been pretty light, with only "3 souls on board" according to the radio.  So essentially an empty aircraft with something like 25,000 lbs of fuel.  That weight would work out to a fairly slow approach speed, but being light weight they could add 10 or 20 knots above what they think their IAS is (converting GS to IAS without having the winds at altitude is where the uncertainty comes in) and fly the faster speed.  With a heavy aircraft, being 20 knots over your target approach speed could make for issues getting the aircraft stopped on the runway, but with the lighter aircraft those issues are much easier to deal with.
From the one radio transmission caught on the video, they evidently did have radio altitudes from the EGPWS, which is a fair proxy for the altimeter -- albeit with limitations.  If the captain was flying the aircraft using the HUD, or if the EFIS displays on that aircraft include a flight-path vector display, then it's entirely possible to maintain level flight, even if what altitude that is can only be surmised.  (They might also have something in the cockpit that displayed GPS altitude for them -- depends on exactly what they had & if they took the time to get to it.)
Also of note, both links state that the aircraft flew out 2 hours later, which would be consistent with a blockage of the pitot-static system that was cleared out fairly quickly, and at that point the jet is good to go.
Final comment: I'll reiterate, I'm NOT posting this as any sort of statement that "this is what must have happened there."  We don't have enough data to reach certain conclusions.  I'm only drawing inferences from what limited information we do have in those 2 links, and suggesting that the scenario I laid out seems to be consistent with what is in the article and the video, and thus seems to be the most likely explanation.  If new facts come to light, anything or everything above could be subject to revision.
From everything I can see, it was a nice job by the crew to bring the aircraft safely back on what had to be a pretty bad day at the office!

I believe that it was a cargo flight, hence the "3 souls on board" -- they probably were fairly heavy...


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How does a jet fighter with water-skis land safely?
I just read about the Convair F2Y on the obvious encyclopedic site. It's a delta wing jet fighter from the 1950's, with hydroskis so it can take off and land on water.
Can such a landing be made reliably safe? What is the angle of attack, landing speed, and other techniques of such a landing? I'm concerned because it's such a small craft, and if the skis catch a wave the wrong way, it cloud flip over and disintegrate. It seems to me that even a tiny amount of waves on the high seas would make this thing very dangerous to land.
It looks like the Convair was canceled for a different kind of accident in mid-air. I could not find how many landings it performed safely. For all I know it could have been only 1 or 2 landings before it was canceled.

Maybe that's why there aren't any fighter jets on skis or floats?

@Ron Beyer: But there are numerous non-fighter aircraft that can land and take off safely from water, and the Russian ekranoplans show that jet engines can be used close to the water.  Indeed, the Russians have developed a jet-powered amphibian, the  Beriev Be-200: https://en.wikipedia.org/wiki/Beriev_Be-200

@jamesqf Right, but they aren't supersonic or near sonic aircraft, they have large floats. I don't think it is a matter of engine placement, but high-drag structures that do nothing more than make the thing float.

@Ron Beyer: But those are different issues.  The question was about whether it was possible to take off and land safely.  Nor do seaplanes necessarily need high-drag structures - the FY2 didn't have them - though I admit I don't know how well a hydrodynamic hull would function at near-sonic or supersonic speeds.

@jamesqf Could a fighter jet be made to take off/land on the water? Sure. It wouldn't be much of a fighter jet though. I guess the round-about point I was trying to make is that you can make it safe as a float plane, but not as a fighter, or you can make it safe/competitive as a fighter, but not as a float plane, at least not with techniques used today. Safest/most competitive way I can think of to do this today is to keep the two structures separate, have it land on the hull, basically an aircraft carrier...

The real reason for the Sea Dart's cancellation was the development of the cantilever flight deck, allowing conventional high performance jet aircraft to operate from carriers. No need to have a fighter that could land on water, and suffer the weight and drag penalty of that capability, plus the need for relatively calm water for takeoff and landing, not to mention the substantially higher maintenance from salt water damage.

See also the Martin P5M SeaMaster bomber, which had a hydrodynamic hull. One problem with that hull was how to develop a bomb bay. The solution, a rotary bomb bay, is in use with the B1 and B2 bombers today.

In the specific case of the F2Y, this video report from the US Navy and General Dynamics shows how it was done.
In the video: It lands on water the same way as any other amphibious aircraft. The only difference is that the engine intakes must be protected from water because too much of it will cause the engine to flame out and shut down.


text:
In an Airbus, if the AOA sensor fails and the computer pitches the plane down, can the computer still only pitch down 10 degrees maximum?
For example, something similar to Qantas Flight 72.
Assuming the Angle of Attack sensors are faulty and give bogus data - for example, that the Angle of Attack is 20 degrees, or the maximum Angle of Attack when the plane is flying normally and in no danger of stalling.
The flight protection systems are going to kick in and try and pitch the plane down because the computers will think the plane is stalling or about to stall because of the (bogus) Angle of Attack readings.
Would the computer still be restricted in how far it can pitch the nose down? For example would it suddenly angle down but stop at 10 degrees nose down, or would it go into a ballistic, unrestricted and dangerously steep dive?
I read a pilot in an Airbus cannot make the plane pitch down more than 10 or so degrees in ''Normal Law'', would this apply if the plane's computers are trying to pitch the plane down due to faulty AOA sensor data?

Maybe I'm misunderstanding the question, but: If the angle of attack data fed into the flight protection systems is wrong -- unknown to the protection system, obviously --, how could it know when the limit is reached? Wouldn't it always think the airplane is pitched at whatever the faulty data indicate and desperately try to "correct" that?

No, Angle of Attack is separate from the Attitude of the plane. Angle of Attack is measuring airflow angle over the wing, wheras Pitch Attitude is the angle of the plane itself relative to the horizon. The Angle of Attack sensor could be saying 20+ degrees but the pilots would still see the Artificial Horizon saying the plane was in level flight as the Artificial Horizon would be unaffected.

Thanks for the clarification. I let the comment stand for others wondering the same though.

The answer below is for the A320, as this is the only Airbus manual I have access to.

would it go into a ballistic, unrestricted and dangerously steep dive

It'd likely stop somewhere before that. "Abnormal attitude law" engages when:

Bank angle above 125°
Pitch above 50° nose up or below 30° nose down
KIAS below 60 to 90, or above 440
Mach above 0.91
AoA above 30° to 40°, or below -10°

I believe the FAC will also give up at some point as the computed KIAS is so far away from what is measured. If it is a double ADR failure or double FAC failure it will go down to Alternate Law. If it is a triple failure it would go to Direct Law, as was the case of GXL888T.

Could you clarify if abnormal attitude law engages when all of those conditions are met, or any of them?

@Jules, any of them (it is the only interpretation that makes any sense).

125° bank angle limit is insanely high. Is there ever a reason to keep running in normal or alternate law with e.g. 90° bank angle?


text:
How can I calculate effective wingspan of a high aspect ratio model airplane?
I've heard of people talking of wingspan and effective wingspan.
Considering:
L = Lift Coefficient . 1/2 Rho . Velocity ^ 2 . Surface Area,
I understand that tip vortices increase drag, but do they reduce the effective wingspan of a wing?
How can this be calculated?

I think the term "effective wingspan" should better be replaced by "effective aspect ratio". There is no change in wingspan when the wing flies closer to the ground, but it behaves like an equivalent one with a higher aspect ratio. The basic formulas can stay unchanged, only aspect ratio should be adjusted.
Think of it this way: If there was an increase in span, would wing area grow with it? Would that mean that wing loading goes down? No, it is better to assume that the wing near to the ground behaves like one of the same area, but of a higher aspect ratio with an increased span and a proportionally shortened chord.
Sighard Hörner gives an approximation on page 7-13 in his book Fluid Dynamic Lift for the increment by which the effective aspect ratio is increased over the geometric aspect ratio:
$$\frac{∆AR}{AR} = 0.09\cdot\frac{h}{b}$$
b is wingspan and h is the height of the aerodynamic center over ground.
He also has graphs for the change in effective aspect ratios of vertical tails with the height at which a horizontal tail is attached, or the effective aspect ratio of a biplane wing:
Plot of effective aspect ratio over geometric aspect ratio of a vertical tail depending on the vertical location of the horizontal tail (picture source)
The case where an effective span makes sense is in the calculation of the induced drag and vortex location of a rounded wingtip. Here is Hörner's list of wingtip shapes from the same book:
Wing-tip shape and tip-vortex location for a family of wings (picture source)
And lastly, no, wingtip vortices don't cause induced drag. It doesn't become true just because it is repeated so often. Please look here or here for a better explanation.


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Why are civilians not allowed to fly demilitarized US fighter jets?
I have seen it is possible to fly demilitarized Russian fighter jets in the US. Why is it impossible to fly American demilitarized fighter jets?

Are you primarily interested in a technical "impossible" (which could, for example, be answered with "no such airframes exist"), or a legal "not allowed" (which could, for example, be answered with pointers to appropriate legal texts)? The difference between the two is significant.

"Impossible" - are you sure?  These folks sell Skyhawks.

Very closely related to this question and this one

I was thinking of the aspect that you need a type rating to legaly fly such a jet. But I did not found any offer, except the airforce, to get a type rating for an american fighter jet

@user18804 The military does not provide type ratings in the sense that the FAA does. In fact military pilots are not certificated pilots at all unless they also hold an FAA license.

That's because US military is particularly concerned about chopping up its assets before civilians can lay their hands on them. The procedures are covered in US DoD Manual 4160.28 Defense Demilitarization: Procedural Guidance.
The procedures for 'demilitarizing' military aircraft are particularly brutal:

Military Aircraft
(a)  Aircraft (Figure 29 and Figure 30) that are specifically designed for military purposes shall be demilitarized as follows:  at a minimum, cut or break completely through at least one lobe of the fuselage trifurcated horizontal and vertical stabilizer spar attachment fittings, on both the right and the left hand sides of the stabilizer carry-through spar assemblies.  This demarcation of the prescribed DEMIL procedures is to ensure the aircraft is rendered unfit for flight.

(emphasis mine).

Demilitarization Procedure; image from Popular Mechanics

(b)  Helicopters (Figure 31) specifically designed for military purposes shall be demilitarized by crushing, shredding, or smelting the entire airframe and fuselage, ensuring that the transmission mounts and supporting structural beams, engine deck in area of mounts, wing attaching mounts and support beam structure, and fuselage to tail boom attaching mounts and tail rotor gear ox mounts have been destroyed.

So basically, it boils down to the fact that the US military makes sure that the airframes won't fly again. Of course, there are ways around this- you can assemble the aircraft from parts or some aircraft will simply escape the procedure and is avialble:

In a letter to the chair of the House Armed Services Committee, AOPA President Phil Boyer ... stressed that certain aircraft (possibly aircraft not demilitarized) had been carefully maintained over the years and were now serving useful purposes.

but these are quite rare.

This isn't always true, there is at least one instance of a privately owned F-16, and others like an F-104, F-86, F-100, T-2 Buckeye, T-38, and F9-F for example. There was also the case of 3 F-14's being sold to private owners that were later seized. The F-14 is a special case though, the US is trying very hard to keep spare parts from getting to Iran.

@RonBeyer Looks like the aircraft in question was a demilitarized one requiring restoration. " What is clear is that Air Capital Warbirds will sell the aircraft, either as it is or as restored.". Of course, this does not discount the fact that some aircraft may slip through the cracks, however unlikely.

Being that, for example, F-16's are flown by 26 different nations, if one had the $$ they could probably get ahold of one. Amy idea what it would take as far as ratings, etc. to fly it in the US?

Ever heard of the Collings Foundation? They have a Phantom that, last I checked, was still flying. And an A-4.

I guess it's the other way around. US Gov does it so we don't got a lot of "used warbirds salesman" not obligated to refuse to sell cheap  airworthy airframes to "anyone"

At one time several (at least 4 or 5) North American F86 Sabra Jets where publicly owned. Though, I have not seen or heard of any recently. A privately owned one was used for a old sci-fi film about post Armageddon ~1965.

As the other have alluded, it is not impossible to fly demilitarized American military aircraft, it's just exceedingly difficult.  Many are just not available due to the government holding the aircraft in reserve, and older ones are often limited by the availability of parts.
The FAA provides guidance for obtaining airworthiness approval for former military aircraft in AC 21-54 which is the first step in being able to fly such an aircraft.
Also as pointed out, the FAA doesn't have type ratings available for the majority of these aircraft so that poses a problem in being able to fly it once it's airworthy.  The FAA addresses this using a Letter of Authorization or LOA.  the process to obtaining this is defined in the following FAA documentation.

There are plenty of ex-military planes from many nations in private hands.
I know of an F4 being restored to flying condition by a private individual.  He claims his will be the second in private hands.
A friend of mine owns an early MiG jet as well as a former Soviet trainer.
There have been several T-38s for sale from various online sources.
There are privately held T-33s out there.
At least one F-86.
A few MiG-21s.
At least one F-100.
At least one F-104.
At least one MiG-29.
At least one Harrier.
At least one F-8.
A couple A-4s.
There is at least one Cobra flying around privately as well.  Saw it a few weeks ago.
The list goes on...
There was a proposal sometime back to convert obsolete A-10s to fire fighting tankers.  The outfit was, shall we say, "well connected" but it ended up not going anywhere.  It would have made a GREAT, albeit pricey, tanker platform if I do say so myself.

Plenty of P-2 Neptunes were converted for fire fighting, too.

The Wikipedia article on the Lockheed F104 Starfighter mentions a privately owned example in the US.


text:
Unlike other sectors, why does aerospace have 'design approval ' phase?
Very basic question:
Why do we need Design approval phase in aerospace? Shouldn't it be the product approval that matters? -> How does design ( 'How we achieve the requirements') matter?
I was working in consumer electronics and I have never heard of this 'design approval'.

The short answer is because consumer electronics rarely kill people if there are flaws in the design.

So does automobile/aero follow the below approach?

Check performance specification
Derive design meeting the specification
Wait for the approval
Once approved start production based on the approved design.

What is production approval, then?

I don't know what the automotive industry does.  There are Federal safety regulations manufacturers are required to follow, but i would imagine there are some differences between industries.

Some electronics are dangerous and have lead to approval process'. Generally killing customers is frowned upon so in industries where its happened the government has stepped in.

Consumer electronics have approval processes. Radio transmitters  require approval from FCC and other national bodies. In North America, UL/ETL/CSA approval (listing) is required by retailers to sell things that plug into the wall. Japan similarly requires PSE approval. The big exception is Europe which only requires self-certification (CE mark).

@DivyaK.S Design approval means the design is safe. Production approval means the items are being produced in accordance to the design. A lot of the reason why it's separate comes from the Soviet Union, where design bureaus and production associations were separate, and from the pre-globalization era where the enterprise spanned national bodies, e.g. Airbus designing in France under DGAC supervision and producing wings in the UK under the CAA. (This all got rolled into the JAA and then EASA)

Design approval is not limited to aviation, it's part of any reasonably mature development process, be it software, airplanes, medical equipment or others.

Remind me never to buy any consumer electronics from a company you have worked for.  I have worked with design approval processes of one kind of another all my working life.

The short answer is because consumer electronics don't kill hundreds of people at a time if there are flaws in the design.
Safety is the main reason why we have the FAA, and design reviews can save costly errors later in prototyping.

“Consumer electronics rarely kill people if there are flaws in the design.”  - shock and electrocution hazards are very common in consumer electronics and do have to be mitigated, particularly with any device connected to mains power or can store large amounts of electrical energy.

@Romeo_4808N, I'm not saying hazards to consumers shouldn't be mitigated, but risk is the product of probability and severity, and a zesty spark from your cell phone is a far cry from killing a few hundred people in a major crash. They really aren't even comparable.

Consumer electronics have some hazardous parts sure, but those hazards can usually be contained to small parts of the overall system, and the response to a fault detection can be to just shut the system off.

@MichaelHall unless zesty sparks from your powerbank are the causes of multiple plan crashes ...

It's mainly because in aircraft design, risk mitigation is built into the basic design, and incorporates various risk mitigation principles such as redundancy, fail passive design, human factors etc, determined by regulatory and industry agreed-upon standards.
For example, there is a detailed system analysis that looks at failure modes, the follow-on effect of failures, the mathematical probability of negative results flowing from failures, that sort of thing.
A risk hierarchy is used, that designates events a Minor, Major, Hazardous, and Catastrophic. Catastrophic is total loss of an airframe due to a single initiating event. The risk requirement for a catastrophic event, following something breaking, is a probability lower than one in a billion. For the lesser categories, the probability level is less onerous.
So the OEM has to submit a design along with a comprehensive analysis, and show in its design that the risk mitigation elements are built into the design to meet the regulator's standards, by justifying that its design choices satisfy the regulatory/industry standards.
The authority might reject the analysis that substantiates as particular design, and demand that redundancy be added by including a backup component or second channel to a system, depending on the risk category it falls under. This all happens during the Design Reviews.
You want all of this worked out beforehand before you start to cut metal, to minimize the chances of unpleasant surprises, so that's the main reason this process is used. The only other industry that follows this sort of design protocol is the nuclear industry, which has more or less adopted aviation risk mitigation standards (carried a little too far some say, which is why it's so difficult to build a new plant in the US).
The 737 Max fiasco was fundamentally a breakdown of the process at the design review/approval stage, where the FAA accepted a failure effects analysis for the MCAS system that was inadequate at risk mitigation (using a single AOA vane channel as an input source). Boeing declared an MCAS failure as equivalent to a Stab Trim runaway, and based the system architecture on the that failure mode (which was only at the Major risk level IIRC). The FAA had gotten too comfortable at accepting Boeing's analysis at face value, even accepting the initial pitch issues found during flight testing.
In addition, when Boeing discovered the issues with MCAS affected a wider envelope than they'd originally told Boeing during flight testing, they hid that from the FAA (why the Chief Test Pilot was charged).
So you could say that the MCAS story demonstrates why this entire protocol is used in the first place, being a demonstration of what happens when it breaks down.

There are sectors that require design approval, like offshore and ship cranes.
Additionally, the design of appliances is currently regulated, see the  webpage of the chinese branch of the German testing company Dekra:

Have their designs met safety standards, such as electrical
insulation, materials, structures, electric leakage, short circuit,
overload, overheating?

In production approval, the company must show they’ll test and verify the product to ensure it meets FAA standards for its particular design and function. The agency will need to ensure that a system for production is in place to verify that each manufactured part matches the FAA-approved design.

[Ref1]
[Ref2]
[Ref 3]
[Ref 4]

This answers "what" the FAA does, but you specifically asked "why".

Please convert the image to text so that it can be searched, and so that it can be read by screen readers for vision-impaired users. Posting an image of text isn't a preferred technique on Stack Exchange boards.


text:
What is the reason for aircraft AC power supply neutral wire not connected to chassis GND?
In home utility power supply, AC neutral and earth GND are connected together at distribution transformer output.

Is there a reason why aircraft power supply is not following the same practice? Why does the aerospace standards specify a strict isolation between neutral and chassis GND?

Note: it is the same on boats, ships, mobile homes, etc. Just lack of ground. Forget the old "there is no absolute potential, but only relative potential". So careful before to plug some devices (which doesn't expect such setup, like many surge protections, and measurement devices).

Electrical engineering question, but here is the idea.
In short
The usual earthing/grounding scheme used in large aircraft is TN-C. T indicates the source has its neutral connected to earth (ground). This scheme is the same than for homes in the US. Earth is used as a protective connection against accidental contact between a phase and an exposed metallic part (e.g. casing).
Isolating neutral from earth is an IT earthing specificity. IT is being used in new and more electric aircraft. I believe the documentation you've seen is related to this IT scheme.
Design differences:

In TN-C, a fault leads by design to a short-circuit between phase and earth, resulting in a current growing to a huge value in the time required for detection and source disconnection. The rate of growth is proportional to the voltage.

In IT earthing a fault is not a short-circuit, and current is limited to a very small value, there is no need to disconnect the source as long as there is a single fault (at the second fault, the source is disconnected).

IT is safer and tolerant to a single fault. More electric aircraft (MEA) which rely on more powerful electric sources, and higher voltages, will use IT earthing instead of TN-C.

What is the point of earthing?
Earthing is a way to protect people against an accidental connection between a phase and exposed conductive parts which are not intended to carry a current, what electricians call a fault. The protection consists in preventing a significant voltage to exist between the exposed parts and the ground.
If this was not prevented, a person in contact with the ground, and at the same time with the exposed part, would create a path for a current between the two contact points. Due to the low body resistivity, this current would usually exceed the lethal combination of 100 mA during 3 seconds. To prevent this, phase faults must be detected, this requires a connection to earth, either at the source point, at the consumption point, or at both.
(Earthing doesn't help protect against touching two phases, or a phase and the neutral.)
Disconnecting or not disconnecting?
Usually the remedy for a phase fault is to disconnect the source before the current raises to a lethal level, this is what is done for home consumers.
But disconnecting the source is something industrialists want to avoid, it means stopping equipments which may be long and costly to restart (e.g. a blast-furnace). Alternate protective measures have been devised, offering protection without disconnection as long as there is only one phase fault. Such tolerant protections cannot be used for home consumers, because they require the low-voltage transformer connecting the grid to the consumer to be dedicated, with its neutral isolated from earth.
Common earthing schemes
All earthing schemes are described in IEC 60364-1, and are known by an abbreviation:

First letter → mode of connection of the source neutral.

Second letter → mode of connection of conductive exposed parts (chassis).

Optional third letter → possible combination of protective conductor with neutral.

Common schemes are (pictures from Schneider Electric):

TT: Source neutral and chassis connected to earth.

If any current leaks to earth through the chassis and/or the body, then this quantity of current flowing through earth is missing in the neutral. If this difference exceeds 30 mA, it triggers a breaker to disconnect the source. Use in most countries in Europe.

TN-C: Source neutral connected to earth, chassis connected to neutral, protective earth combined with neutral into a single wire (PEN).

When a phase leaks into a chassis and earth, a short circuit is created with the neutral, it is detected and remedied by a breaker. Used in the US (and UK in part) for homes.

IT: Source neutral isolated, chassis connected to earth. Used around the world by industrials. The plant has its own transformer, its neutral is nearly-isolated from earth. There is naturally a high-value parasitic impedance between earth and neutral, and often a true fixed impedance (1.5 kΩ) is added to prevent the random change in the potential of the neutral.

When a phase is in contact with a chassis, a current flows through earth, the impedance, and the neutral. However this current is limited by the high-impedance on the neutral to a safe value. It nevertheless creates a detectable voltage at the terminals of the impedance, which is used as an indicator of the fault, but the source is not disconnected.
A second phase in contact with a chassis is still not dangerous for a person, but it creates a short-circuit between phases, this is dangerous for the equipments, the source is disconnected.

Aviation earthing (grounding) schemes
There is no earth connection in an aircraft, but the aircraft conductive structure plays the same role. Earth (ground) continuity is ensured by the metallic elements of the airframe (frames, struts, crossbeams, and metallic skin) and a specific electrical network made of cables (ESN) for composite skins like in the A350 (an electrical continuity must also exist in the composite skin to evacuate static electricity and maintain the electromagnetic shielding against lightning).
The most common scheme in aerospace is TN-C. The documentation you read, which insists on isolating neutral and chassis, is not for TN-C.
There are plans for using an IT scheme. One reason is the use of composites which removes the advantage of having an inexpensive and strong PEN, TN-C can be as well replaced by the more tolerant IT.
IT scheme and Airbus
There is a thesis from Cédric Baumann, in French, about using the IT scheme in aeronautics. It led to a patent now owned by Airbus.
The advantages mentioned in the patent include using the IT scheme for the high-power technical loads (270 VDC/230 VAC) of a more electrical aircraft, the commercial loads (28 VDC/115 VAC) kept for compatibility still using TN-C. This duality allows to introduce some separation in the system. In addition, in TN-C scheme with a powerful source, in case of fault the current between the chassis and earth may reach large values in a short time (short circuit), a problem not found in IT with the high-impedance coupling.
I believe the documentation you have read is related to this IT scheme, not to the usual scheme.
More details about this in Grounding topologies for resilient, integrated composite electrical power systems for future aircraft applications.

It should be mentioned that ships are generally IT for the fault tolerance reasons as well; a single fault is no problem for reliability.


text:
Why is FAA Aircraft Certification Service department named as AIR?
The acronym AIR doesn't match with the functional name "Aircraft Certification Service"
"AIR (the Aircraft Certification Service) is the department within the FAA that develops and administers safety standards for aircraft and related products that are manufactured in the United States or are used by operators of aircraft registered in the United States"

Ref1
Ref2

Because it's not an acronym. It's an administrative designation code for the office. While many are acronyms, others are not. The key is to make sure they are unique across the agency. They are in effect tied to mail distribution in large government buildings. It's a lot easier to write AIR-130 than Aircraft Certification Service, Engineering Directorate.
Once you get out of headquarters, the regional/local offices tend more to the standard acronym for the office: Aircraft Certification Office (ACO), Flight Standards District Office (FSDO), Manufacturing and Inspection District Office (MIDO).
If you dig through the FAA organization you'll see that the major office codes have two common properties: they all start with an "A" and are three characters long.
While Air Traffic Organization (ATO), Human Resource Management (AHR), Commercial Space Transportation (AST), are at least an approximate acronym; Airports (ARP), Finance and Management (AFN), and Aviation Safety (AVS) are more of an abbreviation.
Flight Standards (AFS) and Aircraft Certification Office (AIR) are under AVS.
As to why AIR was chosen, I can only speculate as it was done a very long time ago and from experience in other government agencies, when these are set it's typically some staffer to the front office that proposes the structure and the boss signs off on it. So at most you'll find a directive that says what it is but is unlikely to specify the rational for each.
Personal speculation would be that AIR comes from 'Airworthiness' or looking way back, it was originally the Aeronautics Branch. AIR could be drawn from that or an early mission statement that tied them to 'Inspection and Regulation'. Take your pick.


text:
What exactly is a compressor stall?
I hear the term "compressor stall" when talking about turbine engine difficulties.
What exactly does this mean? And how does a pilot diagnose and fix it - specifically, would there be any changes in the engine instruments compared to normal operation?

That's a lot of questions, I suggest you split them in multiple ones, all together seem a tad too broad for an SE site.

This is a great introductory write-up on the subject, which covers every  question you asked: http://www.b737.org.uk/enginemalfunctions.htm

Compressor stall is already explained at several places on this site, e.g. http://aviation.stackexchange.com/a/11552/524, but I don't think any of them mentions what it looks like on the instrument panel.

This question was cited by this video.

The spinning blades in the compressor stage of a jet engine or turbo fan are themselves airfoils, like the aircraft's wings. The operation of the engine depends on the smooth flow of air over the blades.
Just like a wing, an individual blade, or a small component of one, can experience an airfoil "stall", where the air flow over the blade separates into a cell of "stuck", highly turbulent air behind the blade, and the air flows around the cell instead of smoothly around the blade.
When a flow separation occurs, the airfoil's ability to push the air in proper direction at the right flow rate—and thereby contribute to the compression of air behind the fan assembly—is inhibited.
Since these blades are rotating, the blade quickly moves away from the packet of stagnant air. Of course the stalled air packet has some momentum from the intake air, and it will experience a drift along with the rotating blade, but it is not moving with the average flow of the air through the engine anymore.
Thus the next blade spinning round tends to encounter the stalled air packet. If the stalled air cell is not particularly large, it may be absorbed by the air flow at this stage and dissipated. Alternatively, it might be large enough to stall the subsequent blade as well. At this point, it is called a "rotational stall".
If the stall continues to propagate, the ability of the fan stage to deliver air to the subsequent compression stage is impeded, and it will lead to an abrupt drop in pressure inside the combustion chamber. This causes a reduction in available oxygen for combustion. The engine's performance, measured by the thrust delivered, is strongly impaired, and there is likely to be a lot of unburnt fuel remaining after the oxygen in the compressor is exhausted. That unburnt fuel may ignite in a bright exterior flame as it escapes out the back of the combustion chamber and mixes with the oxygen-rich bypass flow, or in the case of a jet engine, after it exits the engine altogether.
The drop in back pressure in the compressor will, under normal conditions, enable the compressor fan blades to begin operating as proper air foils again.
An alternative type of stall is a compressor surge. In this case, the problem is caused by unexpectedly high pressure in the combustion chamber (or in the compressor), which forces its way forward as well as backwards, against the incoming flow rate. Again, this disrupts the operation of the compressor blades as airfoils.
See Advanced Control of Turbofan Engines by Hanz Richte


text:
Which runway should I have used, and how can I properly choose it in later flights?
Today I wanted to fly and could take off from the runway of my choosing. I have wind from 040 at 13KT and the one runway is 09/27.
Which runway should I use?
I would use runway 09 because an aeroplane should start against the wind, but then I have crosswind, right?

If there is only one runway, then surely you will have crosswind whichever direction you choose? Am I missing a part of your question?

Yes, but if you take off 27, the crosswind will be the least of your problems lol.

What do you mean by "recognise"?

The large number of uv's so far is a bit "interesting"--

I am missing something, there is a crosswind regardless. And how is the runway 'unknown'?

Crosswinds are part of flying, airfields have a limited number of runways but wind can come from any direction, it's rare that wind is straight down the runway.
All airplanes have a demonstrated crosswind limit, determined by the characteristics of the airplane, pilots take that into account as well as runway conditions and their own proficiency when deciding how much crosswind they can tolerate. It's almost always advisable to take off into wind, with the lowest crosswind component, in your case there's only one into wind option which is 09. Winds of 040 at 13 knots would be 50 degrees off the runway, which equates to about 10 knots of crosswind, which it totally doable in any airplane you're likely to fly, with the exception of some tailwheel airplanes.

Better a crosswind with a headwind component, than a crosswind with a tailwind component!
Your only sensible option is runway 09 in the situation you have presented.

As the other answers have indicated, you want to take off into the wind as much as possible (aside from other considerations like runway slope or obstructions). The airplane has a maximum demonstrated crosswind component, but you also need to consider your personal minimums / maximums.
As GdD's answer indicates, this scenario has about 10 kt of crosswind, which is acceptable for most light airplanes. However, if you've always had a direct headwind, or only a few knots of crosswind, this may not be a good day to fly. Or you maybe need to grab a CFI and practice some landings with higher crosswinds than you've seen before.
Many pilots will (or should!) write down their personal mins / maxes, so as to better help adhere to them. Some examples of such mins / maxes might be:

Visibility at least 10 mi
Ceiling at least 15000 ft
No precipitation
Max crosswind at any planned runway less than 5 kt
And so forth

Most of these criteria are more restrictive than the aviation regulations specify, but as a new / student pilot you don't have the experience to fly at minimums. And they mean that there will be days where you won't fly, even though there may be a full pattern at your airport.
As you gain experience and confidence, you will want to adjust your personal minimums - maybe once you've done 3 (good!) landings with a CFI in a crosswind of 8 kt, you increase your personal max crosswind component from 5 kt to 8 kt. If you haven't flown for some time, you may want to make your personal minimums more restrictive, too. These are not set in stone, and can (and should!) change as your experience, knowledge, confidence, and currency changes.

Great reminder that personal minima do not have to be as high as legal minima. Know your limits and live within them. Exceeding them may be bad for your health.

All else being equal, yes, you should takeoff into the wind as much as you can. However, depending on the airfield, there may be other factors such as terrain obstructions and runway slope that skew this decision.

With wind from 040, the ideal runway is 04—just drop the last zero.
However, most of the time you won’t be so lucky as to have an ideal runway available, which means dealing with some amount of crosswind.
Of the runways actually available at your airport, 09 is closer to 04 than 27 (on the compass or DG/HSI), so that is probably the better option.
Note that wind is just one factor; there may be other factors, such as terrain, traffic, ATC, length or surface that dictates using a different option.  You should practice crosswind and tailwind landing with your instructor to be ready for those cases.


text:
When ATC tells you to climb or descent now, do the speed restrictions on SIDs and STARs still apply? (EASA)

I am flying the ELSUP 1H departure. After taking off, I get told to climb to FL100. Do I have to comply with the speed restrictions? Is it the same for a STAR?

According to Canadian rules, Yes. I will do more research and try to make my answer more relevant to this particular question but as of now what follows is based on Canadian CARs.
Unless specifically stated in the clearance, the balance of the SID remains unchanged despite ATC revision of a component.
According the the Transport Canada AIM (eff. 0901z March 21, 2024 - 0901z October 3, 2024):

A SID termination fix may be a NAVAID, intersection, or DME and is normally located on an established airway where the SID terminates and the en route phase of flight commences. The SID, as published, contains an altitude to climb to after departure; however, ATC may assign an altitude different from the altitude specified in the SID, provided the altitude is stated and a readback is obtained from the pilot prior to departure. In addition, where vector SIDs are used, ATC may assign a different initial departure heading. However, an ATC revision to any item of a SID does not cancel the SID.

The same applies for a STAR. Not only does amending one component not affect others but the pilot is also expected to re-intercept the STAR profile when given a partial deviation from the charted route.
From TC AIM Section 9.2.3.15 “Amending Routes”:

ATC may amend STAR routes by clearing the aircraft direct to a waypoint depicted within the STAR. ATC will confirm what to expect if they intend for the aircraft to rejoin the STAR procedure when initiating vectors. When an aircraft is cleared direct to a STAR/approach interface waypoint, unless it is cleared for an approach, the pilot shall proceed direct to the STAR waypoint, and not to the approach waypoint, to re-intercept the STAR profile.

Note: an ATC revision to a charted restriction supersedes all of the other charted restrictions of the same kind, eg. an ALT revision supersedes all other charted ALT restrictions, speed for speed and so on.
The STAR is cancelled either explicitly by ATC along with vectors/WPTs to follow thereon or when an approach clearance is issued.

References:
SID - TC AIM
IFR - Arrival Procedures - TC AIM

Your answer may well be correct, but it's hard to tell since you are referring to Canadian rules despite the question being about EASA.

@60levelchange Question didn’t mention EASA when I answered, although I guess I could’ve taken a closer look to where it says “EPPO” :-P

The answer is yes in both cases. ICAO PANS-ATM (Doc 4444) is mentioning:

4.6.4 SID and STAR
The flight crew shall comply with published SID and STAR speed restrictions unless the restrictions are explicitly cancelled or amended by the controller.

The phraseology for cancelling the restriction is also described in PANS-ATM. For SIDs:

6.3.2.4.1 Clearances to aircraft on a SID with remaining published level and/or speed restrictions shall indicate if such restrictions are to be followed or are cancelled. The following phraseologies shall be used with the following meanings:
[...]
d) CLIMB VIA SID TO (level), CANCEL SPEED RESTRICTION(S):
[...]
e) CLIMB VIA SID TO (level), CANCEL SPEED RESTRICTION(S) AT (point(s)):
[...]

Likewise for a STAR

6.5.2.4.1 Clearances to aircraft on a STAR with remaining published, level and/or speed restrictions shall indicate if such restrictions are to be followed or are cancelled. The following phraseologies shall be used with the following meaning:
[...]
d) DESCEND VIA STAR TO (level), CANCEL SPEED RESTRICTION(S):
[...]
e) DESCEND VIA STAR TO (level), CANCEL SPEED RESTRICTION(S) AT (point(s)):
[...]

d) is to cancel all speed restrictions of a SID/STAR. e) will be issued in order to cancel speed restriction at specific points.
You mentioned EASA. EASA has not incorporated this specific phraseology into SERA yet, although while researching for this answer, I found an amendment proposal to incorporate it to a future release.
EASA regulations take precedence over ICAO regulations; they don't completely replace them. If there is no reference to a subject in EASA SERA, then ICAO regulations are in force for that subject.


text:
Are there documented taxi incidents that could have been prevented by "Follow the greens"?
Upon receipt of taxi instructions at large airports, do pilots ever forget or misremember these instructions, are there any documented instances of this and how much better is a 'follow the greens' type procedure for your workload and memory.
I'm concerned primarily with human memory limitations and how simply following a green centreline reduces the human workload on pilots.
I understand pilots have kneeboards and maps which certainly reduces risk of this happening but it would be interesting to hear if this is possible / has happened before ?

Some airports have "follow me" cars to help pilots navigate complex taxiway systems. A lot less high tech, no idea how effective it is, but supposedly the driver is more familiar with the airport so is less likely to get things wrong. A bit like maritime pilots, but without actually boarding or piloting the plane, just showing the way.

Anything that might go wrong, probably has, in the history of aviation, and things like mis-remembering a taxi clearance has certainly happened a lot.
If by "follow the greens" you're referring to a system that activates the in-pavement centerline lighting, segment by segment, for each aircraft's specified route, that would be very cool and an absolute game-changer. I fly to major airports in the U.S. every week, and I've yet to see such a system in use for getting you from the gate to the runway or vice versa.
If the clearance is longer than about two taxiways (i.e., leave the ramp on A, right turn on B to runway 28), I'll typically highlight the taxi route on the airport diagram on my EFB before starting to taxi. If the clearance is particularly long (Chicago O'Hare is notorious for this), I'll either write it down first, or type it into the FMC scratchpad to refer to as I'm highlighting. And, always, confirm with the other pilot what we're about to do.
And every so often, we still have to ask Ground to repeat or clarify some part of it. Which works fine.
But unless it's the exact same clearance as the last fifty times I've taxied here, trusting memory for a lengthy set of instructions is setting yourself up for a mistake.

Wow I've never seen an airport as complex as ORD until now that's a great example I can use. "follow the greens" refers to A-SMGCS level 4 equipped airports which includes conflict resolution, automatic planning & guidance. But I'm surprised to hear somewhere as busy as Chicago doesn't have this. The results from tests in Europe at least show massive decreases in fuel consumption, better pilot SA and less controller workload.

@Dylan massively expensive, and such things in aviation take time to be adopted.

An example of follow the greens at Incheon Airport in Korea. Eurocontrol has standard phraseology for this e.g. “Callsign, Follow the Greens to Holding Point N2 Runway 27 (or Stand 123).”

That video suggests it reduced the 'mis-entry into taxiway' statistics from 8.8 per month to 1.8 per month, a 70% drop.

The worst aviation accident in Italy occurred in 2001 at Milano Linate airport, on the ground.
A taxiing Cessna Citation crossed the runway after a taxiway error, on a foggy day at the same time a MD-87 was taking off. The Citation pilot had taken R6 instead of R5 at this branch:

Source: ANSV Investigation report.
From the investigation report:

The obvious consideration is that the human factor related action of the Cessna crew – during low visibility conditions - must be weighted against the scenario that allowed the course of events that led to the fatal collision; equally it can be stated that the system in place at Milano Linate airport was not geared to trap misunderstandings, let alone inadequate procedures, blatant human errors and faulty airport layout.

The clearance was not long:

DeltaVictorXray taxi north via Romeo 5, QNH 1013, call me back at the stop bar of the…main runway extension.

But the readback was not compliant, neither mentioning north or the stopbar:

Roger via Romeo 5 and…1013 and call you back before reaching main runway.

This case was a combination of errors and technical failures, despite the airport being one of the busiest in Italy. A visual path of some sort would have been sufficient to neutralize the problems and prevent the fatal consequences.
There is an episode of Air Crash Investigation about it: The Invisible Plane.
More about A-SMGCS and SMAN systems:

Are interlocked "traffic signals" possible/in use for taxiing?

What is the Surface Management (SMAN) all about?

On Linate, the stop bars were malfunctioning and they were so used to this that nobody cared.  So while it is a great example of how taxiway confusion can lead to an accident, it's not so clear that more technology would have changed anything.

I think using a different font for the markings could have changed things; to me "5" and "6" look too similar on the photo.

@Geir: The stop bars were permanently ON, meaning mandatory stop, the pilot didn't not call back when reaching (the wrong) one, as required by the clearance. The stop bars played no role. After the accident, the taxi procedure was changed: "without ground radar functioning [...] with visibility less than 200 meters [...] only one movement at a time shall be allowed on the movement area with the assistance of the Follow-me to comply with national regulation, and is more or less the same than a visual guidance, confirming this system could help change the outcome.